As a species, our family tree extends back in time hundreds of thousands of years, with so many offshoots and splits that it’s hard to keep them all straight. A new study of 28 ancient people found in a Spanish cave has made this family tree even older and more complicated than previously believed.

The DNA of these ancient individuals, whose bones were discovered 30 years ago, has been meticulously analyzed and revealed to be the oldest ever found, The Christian Science Monitor reported. The implications of this discovery are that humans’ branch of the family tree split from the Neanderthals much earlier than previously believed.

The 28 ancient people whose DNA was analyzed were found in a Spanish cave called Sima de los Huesos, or “pit of bones,” located in the Atapuerca mountains. The burial site is a 40-foot-deep shaft, and anthropologists believe the individuals were intentionally buried there 400,000 years ago; they’ve also theorized that they fell to their deaths, Scientific American added.

The skulls of these individuals, referred to as Sima hominins, looked like Neanderthals. They had the prominent brow ridge and other traits. But other features cast doubt on their origins, and some researchers thought they belonged to a much older species — Homo heidelbergensis.

So, their DNA was analyzed and in 2013, the results were revealed. The analysis found that the mitochondrial DNA (which comes just from the mother) in at least one person was closely related to another branch on the family tree called the Denisovans, and not to European Neanderthals. The Denisovans lived in Asia more than 50,000 years ago, BBC added.

But recent, more in-depth analysis has revealed that, in fact, these people represent the oldest Neanderthals ever found.

This discovery was made by looking at nuclear DNA, which contains more lineages than the mitochondrial. Scientists examined five different samples, which likely represent five different individuals. Extracting and analyzing this DNA is very difficult, but the teeth and shoulder blade tissue used had been refrigerated to preserve it.

And it worked, and researchers found out what the skulls had suggested: the Sima hominins are actually the oldest Neanderthals in the world.

At the same time, scientists have been able to recreate the timeline of human evolution a bit. Since these ancient individuals are the oldest of their kind around, they push back the time at which modern humans split off and went their own way down the evolutionary road.

Their age hints that our ancestors split from Neanderthals between 550,000 and 765,000 years ago. That date means one of the oldest human species known, Homo heidelbergensis, couldn’t be our common ancestor.

Whoever this individual is, they likely lived somewhere between 700,000 to 900,000 years ago. Thanks to the revelations uncovered by the oldest hominin DNA found, palaeoanthropologist Maria Martinón-Torres believes that ancestor is likely Homo antecessor. His remains have been found in Spain.

As for the Sima hominins’ link to the Denisovans, molecular biologist Matthias Meyer thinks that their ancestor carried the same mitochondrial DNA, but it was replaced by an as-yet unknown new species that came from Africa and bred with Neanderthals. Their split on the family on the family tree has been pushed back, too.

The discovery of the oldest Neanderthal DNA ever found, and the method by which researchers analyzed the ancient DNA with cutting-edge methods, is fascinating to palaeoanthropologist Chris Stringer. Discoveries like this latest one are proving that science can illuminate the oldest reaches of humans’ ancient family tree.

“It’s fascinating and keeps us all on our toes trying to make sense of it all. Instead of just being stuck with trying to resolve the last 100,000 years, we can really start to put some dates from DNA further down the human tree.”